Current mode control type switching power supply device

ABSTRACT

A switching power supply device includes a first switch, a second switch, a current sensing portion configured to sense current flowing in the second switch, and a controller configured to control the first and second switches in accordance with the current sensed by the current sensing portion. The controller includes an accumulating portion configured to accumulate information of the current sensed by the current sensing portion during a predetermined period of time while the first switch is in the off state, and reflecting portion configured to start the transmission of the current information accumulated by the accumulating portion before the first switch is changed from the off state to the on state so as to reflect the current information accumulated by the accumulating portion on the slope voltage, and controls the first and second switches in accordance with the slope voltage.

CROSS-REFERENCE TO RELATED APPLICATIONS

This nonprovisional application claims priority under 35 U.S.C. § 119(a)on Patent Application No. 2014-194209 filed in Japan on Sep. 24, 2014,Patent Application No. 2014-194211 filed in Japan on Sep. 24, 2014,Patent Application No. 2014-194215 filed in Japan on Sep. 24, 2014, andPatent Application No. 2014-194230 filed in Japan on Sep. 24, 2014, theentire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a current mode control type switchingpower supply device that can perform a step down operation for steppingdown an input voltage.

Description of Related Art

Control methods of switching power supply devices can be roughly dividedinto a voltage mode control and a current mode control. In general, thecurrent mode control is very effective in view of simplification ofphase compensation, fast response, and reduction of the number ofexternal components. An example of the current mode control typeswitching power supply device is shown in FIG. 14.

A switching power supply device 100 shown in FIG. 14 senses currentflowing in an upper metal oxide semiconductor (MOS) transistor Q1 so asto perform the current mode control. In accordance with the current modecontrol, the upper MOS transistor Q1 and a lower MOS transistor Q2 arecomplementarily turned on and off, and an input voltage V_(IN) isconverted into a pulse-like switched voltage V_(SW) by this switchingoperation. Then, the switched voltage V_(SW) is smoothed by an inductorand an output capacitor and is converted into an output voltage V_(OUT)lower than the input voltage V_(IN).

When the current flowing in the upper MOS transistor Q1 is sensed so asto perform the current mode control, a fed-back portion of the currentcorresponds to a difference between the input voltage and the switchedvoltage (V_(IN)−V_(SW)), and hence a current sensing circuit generatesinformation of the sensed current with respect to the input voltageY_(IN). Accordingly, when the current information is transmitted to aslope circuit configured to generate a slope voltage V_(SLP) withrespect to an internal source voltage, there occurs a delay time D afterthe upper MOS transistor Q1 is turned on until the current informationis transmitted to the slope voltage V_(SLP), as shown in FIG. 15.

In addition, because the fed-back portion of the current corresponds tothe difference between the input voltage and the switched voltage(V_(IN)−V_(SW)), if noise is added to a leading edge or the like of theswitched voltage V_(SW), the noise is transmitted as it is and isreflected on the slope voltage V_(SLP).

Further, when a pulse width of the switched voltage V_(SW) is decreased,the above-mentioned delay time and noise become dominant, and thereoccurs a problem that current feedback cannot be performed.

Note that the current mode control type switching power supply devicedisclosed in JP-A-2010-220355 also performs the current mode control bysensing current flowing in an upper switching element similarly to theswitching power supply device 100 shown in FIG. 14, and hence has thesame problem.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a current modecontrol type switching power supply device that can perform currentfeedback even if a ratio of an output voltage to an input voltage issmall.

<First Technical Feature>

Among the current mode control type switching power supply devicesdisclosed in this specification, the current mode control type switchingpower supply device having the first technical feature includes a firstswitch having a first terminal connected to a first application terminalto which an input voltage is applied, a second switch having a firstterminal connected to a second terminal of the first switch and a secondterminal connected to a second application terminal to which apredetermined voltage lower than the input voltage is applied, a currentsensing portion configured to sense current flowing in the secondswitch, and a controller configured to control the first switch and thesecond switch in accordance with current sensed by the current sensingportion. The controller includes an accumulating portion configured toaccumulate information of the current sensed by the current sensingportion during a predetermined period of time while the first switch isin the off state, and a reflecting portion configured to start thetransmission of the current information accumulated by the accumulatingportion before the first switch is changed from the off state to the onstate so as to reflect the current information accumulated by theaccumulating portion on the slope voltage, and controls the first switchand the second switch in accordance with the slope voltage.

<Second Technical Feature>

Among the current mode control type switching power supply devicesdisclosed in this specification, the current mode control type switchingpower supply device having the second technical feature includes thefirst switch having the first terminal connected to the firstapplication terminal to which the input voltage is applied, the secondswitch having the first terminal connected to the second terminal of thefirst switch and the second terminal connected to the second applicationterminal to which a predetermined voltage lower than the input voltageis applied, the current sensing portion configured to sense currentflowing in the second switch, and the controller configured to controlthe first switch and the second switch in accordance with the currentsensed by the current sensing portion. The controller includes a slopevoltage generating portion configured to accumulate, during apredetermined period of time while the first switch is in the off state,information of the current sensed by the current sensing portion so asto generate a slope voltage based on the accumulated currentinformation, and controls the first switch and the second switch inaccordance with the slope voltage.

<Third Technical Feature>

Among the current mode control type switching power supply devicesdisclosed in this specification, the current mode control type switchingpower supply device having the third technical feature includes thefirst switch having the first terminal connected to the firstapplication terminal to which the input voltage is applied, the secondswitch having the first terminal connected to the second terminal of thefirst switch and the second terminal connected to the second applicationterminal to which a predetermined voltage lower than the input voltageis applied, the current sensing portion configured to sense currentflowing in the second switch, and the controller configured to controlthe first switch and the second switch in accordance with the currentsensed by the current sensing portion. The controller includes anaccumulating portion configured to accumulate information of the currentsensed by the current sensing portion during a constant of time whilethe first switch is in the off state, and the reflecting portionconfigured to reflect the current information accumulated by theaccumulating portion on the slope voltage, and controls the first switchand the second switch in accordance with the slope voltage.

<Fourth Technical Feature>

Among the current mode control type switching power supply devicesdisclosed in this specification, the current mode control type switchingpower supply device having the fourth technical feature includes thefirst switch having the first terminal connected to the firstapplication terminal to which the input voltage is applied, the secondswitch having the first terminal connected to the second terminal of thefirst switch and the second terminal connected to the second applicationterminal to which a predetermined voltage lower than the input voltageis applied, the current sensing portion configured to sense currentflowing in the second switch, and the controller configured to controlthe first switch and the second switch in accordance with the currentsensed by the current sensing portion. The controller includes anaccumulating portion configured to accumulate information of the currentsensed by the current sensing portion during a predetermined period oftime while the first switch is in the off state, a reflecting portionconfigured to reflect the current information accumulated by theaccumulating portion on the offset voltage of the slope voltage, and agradient setting portion configured to set a constant slope gradient ofthe slope voltage, and controls the first switch and the second switchin accordance with the slope voltage.

Meanings and effects of the present invention will become apparent fromthe description of embodiments given below. However, the embodimentsdescribed below are merely examples of the present invention. Thepresent invention and meanings of terms of structural elements are notlimited to those shown in the embodiments described below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an example of a general structure of a firstembodiment of a switching power supply device.

FIG. 2 is a diagram showing a structural example of a current sensingcircuit and a slope circuit.

FIG. 3A is a diagram showing a structural example of a voltage currentconversion circuit 4A.

FIG. 3B is a diagram showing a structural example of a voltage currentconversion circuit 5A.

FIG. 4A is a timing chart showing an operation example of the switchingpower supply device.

FIG. 4B is a timing chart showing a variation of the operation exampleshown in FIG. 4A.

FIG. 5A is a timing chart showing another operation example of theswitching power supply device.

FIG. 5B is a timing chart showing of a variation of the operationexample shown in FIG. 5A.

FIG. 6A is a timing chart showing still another operation example of theswitching power supply device.

FIG. 6B is a timing chart showing a variation of the operation exampleshown in FIG. 6A.

FIG. 7 is a diagram showing of a schematic waveform of a slope voltagehaving slope gradient on which current information is reflected.

FIG. 8 is a diagram showing a schematic waveform of a slope voltagehaving a slope offset voltage on which the current information isreflected.

FIG. 9 is a diagram showing another structural example of the currentsensing circuit and the slope circuit.

FIG. 10 is a timing chart showing still another operation example of theswitching power supply device.

FIG. 11 is a diagram showing a general structural example of a secondembodiment of the switching power supply device.

FIG. 12A is a timing chart showing an example of determination as to aratio of an output voltage to an input voltage.

FIG. 12B is a timing chart showing another example of determination asto the ratio of the output voltage to the input voltage.

FIG. 13 is an outside view showing a structural example of a vehicle inwhich in-vehicle equipment is mounted.

FIG. 14 is a diagram showing an example of a current mode control typeswitching power supply device.

FIG. 15 is a timing chart showing an operation example of the switchingpower supply device shown in FIG. 14.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS General Structure(First Embodiment)

FIG. 1 is a diagram showing an example of a general structure of a firstembodiment of a current mode control type switching power supply device.A switching power supply device 101 of this structural example is acurrent mode control type switching power supply device that performs astep down operation for stepping down an input voltage and includes atiming control circuit 1, an upper MOS transistor Q1, a lower MOStransistor Q2, an inductor L1, an output capacitor C1, voltage dividingresistors R1 and R2, an error amplifier 2, a reference voltage source 3,a current sensing circuit 4, a slope circuit 5, a comparator 6, and anoscillator 7.

The timing control circuit 1 controls on and off of the upper MOStransistor Q1 and on and off of the lower MOS transistor Q2, andgenerates a gate signal G1 of the upper MOS transistor Q1 and a gatesignal G2 of the lower MOS transistor Q2 in accordance with a set signalSET and a reset signal RESET.

The upper MOS transistor Q1 is an N-channel MOS transistor as an exampleof an upper switch configured to make and break a current path from aninput voltage application terminal applied with an input voltage V_(IN)to the inductor L1. A drain of the upper MOS transistor Q1 is connectedto the input voltage application terminal applied with the input voltageV_(IN). A source of the upper MOS transistor Q1 is connected to aterminal of the inductor and a drain of the lower MOS transistor Q2. Agate of the upper MOS transistor Q1 is provided with the gate signal G1from the timing control circuit 1. The upper MOS transistor Q1 is turnedon when the gate signal G1 is high level and is turned off when the gatesignal G1 is low level.

The lower MOS transistor Q2 is an N-channel MOS transistor as an exampleof a lower switch configured to make and break a current path from aground terminal to the inductor L1. The drain of the lower MOStransistor Q2 is connected to the terminal of the inductor and thesource of the upper MOS transistor Q1 as described above. A source ofthe lower MOS transistor Q2 is connected to the ground terminal. A gateof the lower MOS transistor Q2 is supplied with a gate signal G2 fromthe timing control circuit 1. The lower MOS transistor Q2 is turned onwhen the gate signal G2 is high level and is turned off when the gatesignal G2 is low level. Note that a diode can be used instead of thelower MOS transistor Q2 as the lower switch, but in this case, it isnecessary to dispose a sense resistor connected in series to the diodeso that the current sensing circuit 4 senses a voltage between both endsof the sense resistor.

The upper MOS transistor Q1 and the lower MOS transistor Q2 arecomplementarily turned on and off by control by the timing controlcircuit 1. In this way, a pulse-like switched voltage V_(SW) isgenerated at a connection node between the upper MOS transistor Q1 andthe lower MOS transistor Q2. Note that it is preferred to set a deadtime in which both the upper MOS transistor Q1 and the lower MOStransistor Q2 are off when on/off states of the upper MOS transistor Q1and the lower MOS transistor Q2 are exchanged.

The inductor L1 and the output capacitor C1 smooth the pulse-likeswitched voltage V_(SW) so as to generate an output voltage V_(OUT) andsupply the output voltage V_(OUT) to an application terminal of theoutput voltage V_(OUT).

The voltage dividing resistors R1 and R2 divide the output voltageV_(OUT) so as to generate a feedback voltage V_(FB).

The error amplifier 2 generates an error signal V_(ERR) corresponding toa difference between the feedback voltage V_(FB) and a reference voltageoutput from the reference voltage source 3.

The current sensing circuit 4 senses current flowing in the lower MOStransistor Q2 on the basis of a drain-source voltage when the lower MOStransistor Q2 is on, namely a voltage between both ends of an onresistor of the lower MOS transistor Q2.

The slope circuit 5 generates and outputs a slope voltage correspondingto the current flowing in the lower MOS transistor Q2 sensed by thecurrent sensing circuit 4.

The comparator 6 compares the output voltage of the slope circuit 5 withthe error signal V_(ERR) so as to generate the reset signal RESET as acomparison signal. Because a slope voltage V_(SLP) generated by theslope circuit 5 has a fixed period, the reset signal RESET becomes apulse width modulation (PWM) signal.

The oscillator 7 generates the set signal SET that is a clock signalhaving a predetermined frequency.

<First Generation Example of Slope Voltage>

FIG. 2 is a diagram showing a structural example of the current sensingcircuit 4 and the slope circuit 5. In the example shown in FIG. 2, thecurrent sensing circuit 4 is constituted of the voltage currentconversion circuit 4A. In addition, in the example shown in FIG. 2, theslope circuit 5 is constituted of switches S1 to S3, capacitors C2 andC3, and a voltage current conversion circuit 5A.

Each of the voltage current conversion circuits 4A and 5A is a circuitdriven by an internal source voltage V_(CC) generated in an integratedcircuit (IC) including the timing control circuit 1, the error amplifier2, the reference voltage source 3, the current sensing circuit 4, theslope circuit 5, the comparator 6, and the oscillator 7.

The voltage current conversion circuit 4A converts a drain-sourcevoltage of the lower MOS transistor Q2 into current and outputs thecurrent. When the switch S1 is on, the capacitor C2 is charged by outputcurrent of the voltage current conversion circuit 4A. On the other hand,when the switch S2 is on, the capacitor C2 is discharged.

The voltage current conversion circuit 5A converts a charge voltageV_(CRG) of the capacitor C2 into current and outputs the current. Theoutput current of the voltage current conversion circuit 5A charges thecapacitor C3. On the other hand, when the switch S3 is on, the capacitorC3 is discharged. A charge voltage of the capacitor C3 becomes the slopevoltage V_(SLP).

FIGS. 3A and 3B are diagrams showing structural examples of the voltagecurrent conversion circuits 4A and 5A. In the voltage current conversioncircuit shown in FIG. 3A, a current source 8 supplies current to acurrent mirror circuit constituted of N-channel MOS transistors Q3 andQ4. If a mirror ratio of the current mirror circuit constituted of theN-channel MOS transistors Q3 and Q4 is 1:1, current flowing in aresistor R4 has a value obtained by dividing the switched voltage Vsw bya difference (r3−r4) between a resistance value r3 of a resistor R3 anda resistance value r4 of the resistor R4. Further, the current mirrorcircuit constituted of P-channel type MOS transistors Q5 and Q6 outputscurrent corresponding to the current flowing in the resistor R4 (currentcorresponding to the switched voltage Vsw as the input voltage of thevoltage current conversion circuit 4A) as the output current of thevoltage current conversion circuit 4A. In the voltage current conversioncircuit shown in FIG. 3B, current corresponding to the input voltage ofthe voltage current conversion circuit flows in a resistor R5 by aseries circuit of the resistor R5 and a PNP transistor Q7, and a voltagecorresponding to the input voltage of the voltage current conversioncircuit is generated at a connection node between the resistor R5 andthe PNP transistor Q7. Further, current corresponding to the voltage atthe connection node between the resistor R5 and the PNP transistor Q7(voltage corresponding to the input voltage of the voltage currentconversion circuit) flows in a resistor R6 by a series circuit of an NPNtransistor Q8 and the resistor R6. Further, a current mirror circuitconstituted of P-channel type MOS transistors Q9 and Q10 outputs currentcorresponding to the current flowing in the resistor R6 (currentcorresponding to an input voltage V of the voltage current conversioncircuit 5A) as the output current of the voltage current conversioncircuit.

FIG. 4A is a timing chart showing an operation example of the switchingpower supply device 101.

In the example shown in FIG. 4A, the timing control circuit 1 switchesthe gate signal G1 from low level to high level when the set signal SETis switched from low level to high level, and switches the gate signalG1 from high level to low level when the reset signal RESET is switchedfrom low level to high level. The slope circuit 5 changes on and off ofthe switches S1 to S3 in accordance with an instruction from the timingcontrol circuit 1.

When the reset signal RESET is switched from low level to high level (attiming t11), the slope circuit 5 maintains the off state of the switchS1, changes the switch S2 from the off state to the on state, andchanges the switch S3 from the off state to the on state. In this way,the capacitors C2 and C3 are discharged, and each of the charge voltageV_(CRG) of the capacitor C2 and the slope voltage V_(SLP) becomes zero.

Then, the slope circuit 5 changes the switch S2 from the on state to theoff state so as to finish discharging the capacitor C2. After that, attiming t12, the slope circuit 5 changes the switch S1 from the off stateto the on state. The timing t12 can be, for example, the end timing ofthe dead time just after the upper MOS transistor Q1 is switched fromthe on state to the off state.

Next, at timing t13, the slope circuit 5 changes the switch S1 from theon state to the off state. The timing t13 can be, for example, the starttiming of a dead time just after the lower MOS transistor Q2 is switchedfrom the on state to the off state.

During the period from the timing t12 to the timing t13, a current pathfrom a voltage current conversion circuit 4A to the capacitor C2 isformed by the switch S1, and hence information of the current flowing inthe lower MOS transistor Q2 is accumulated in a form of the chargevoltage V_(CRG).

After that, when the set signal SET is switched from low level to highlevel (at timing t14), the slope circuit 5 changes the switch S3 fromthe on state to the off state. During the period from the timing t14 tothe next timing t11 (while the upper MOS transistor Q1 is on), theoutput current of the voltage current conversion circuit 5A charges thecapacitor C3, and hence the information of the current flowing in thelower MOS transistor Q2 during the period from the timing t12 to thetiming t13 is transmitted and reflected on the slope voltage V_(SLP).

According to the switching power supply device 101, the fed-back portionof the current corresponds to a difference (V_(SW)−GND) between theswitched voltage V_(SW) and the ground voltage. Accordingly, both thecurrent sensing circuit 4 and the slope circuit 5 can be operated on thebasis of the internal source voltage V_(CC) like this generation exampleof the slope voltage, and hence a delay time that can be generated whenthe current sensing circuit 4 transmits the current information to theslope circuit 5 can be decreased.

In addition, in this generation example of the slope voltage, becausethe information of the current flowing in the lower MOS transistor Q2 isaccumulated in a form of the charge voltage V_(CRG) during the periodfrom the timing t12 to the timing t13, even if noise is applied to aleading edge or the like of the switched voltage V_(SW), the noise isaveraged during the period from the timing t12 to the timing t13. Inother words, amount of noise per unit time that is transmitted andreflected on the slope voltage V_(SLP) can be reduced.

According to this generation example of the slope voltage, currentfeedback can be performed even if a ratio of the output voltage V_(OUT)to the input voltage V_(IN) is small (even if a pulse width of theswitched voltage V_(SW) is small).

Further, in view of stabilizing control system of the current modecontrol, it is preferred to dispose a superimposing portion in the slopecircuit 5, so that the superimposing portion generates a voltage (a newslope voltage V_(SLP′)) in which a sawtooth wave-like or trianglewave-like pseudo slope voltage V_(S) increasing at a constant rateduring the period from the timing t14 to the timing t11 is superimposedon the slope voltage V_(SLP), and to output the new slope voltageV_(SLP′) as the output voltage of the slope circuit 5. In this case, asshown in FIG. 4B, when the slope voltage V_(SLP′) exceeds the errorsignal V_(ERR), the reset signal RESET is switched from low level tohigh level.

<Second Generation Example of Slope Voltage>

Structures of the current sensing circuit 4 and the slope circuit 5 arethe same as those in the first generation example of the slope voltagedescribed above.

FIG. 5A is a timing chart showing another operation example of theswitching power supply device 101.

In the example shown in FIG. 5A, the timing control circuit 1 switchesthe gate signal G1 from low level to high level when the set signal SETis switched from high level to low level, and switches the gate signalG1 from high level to low level when the reset signal RESET is switchedfrom low level to high level. The slope circuit 5 changes on and off ofthe switches S1 to S3 in accordance with an instruction from the timingcontrol circuit 1.

When the reset signal RESET is switched from low level to high level (attiming t21), the slope circuit 5 maintains the off state of the switchS1, changes the switch S2 from the off state to the on state, andchanges the switch S3 from the off state to the on state. In this way,the capacitors C2 and C3 are discharged, so that each of the chargevoltage V_(CRG) of the capacitor C2 and the slope voltage V_(SLP)becomes zero.

Then, the slope circuit 5 changes the switch S2 from the on state to theoff state so as to finish discharging the capacitor C2. After that, theslope circuit 5 changes the switch S1 from the off state to the on stateat timing t22. The timing of t22 can be the end timing of the dead timejust after the upper MOS transistor Q1 is switched from the on state tothe off state, for example.

Next, at timing t23, the slope circuit 5 changes the switch S1 from theon state to the off state. The timing of t23 can be the start timing ofa dead time just after the lower MOS transistor Q2 is switched from theon state to the off state, for example.

Because the current path from the voltage current conversion circuit 4Ato the capacitor C2 is formed by the switch S1 during the period fromthe timing t22 to the timing t23, the information of the current flowingin the lower MOS transistor Q2 is accumulated in a form of the chargevoltage V_(CRG).

After that, when the set signal SET is switched from low level to highlevel (at timing t24), the slope circuit 5 changes the switch S3 fromthe on state to the off state. During the output current of the voltagecurrent conversion circuit 5A charges the capacitor C3 during the periodfrom the timing t24 to the next timing t21, the information of thecurrent flowing in the lower MOS transistor Q2 during the period fromthe timing t22 to the timing t23 is transmitted and reflected on theslope voltage V_(SLP).

In the first generation example of the slope voltage described above,transmission of the information of the current flowing in the lower MOStransistor Q2 is started so as to be reflected on the slope voltageV_(SLP) at the same time when the upper MOS transistor Q1 is switchedfrom the off state to the on state. In contrast, in this generationexample of the slope voltage, the transmission of the information of thecurrent flowing in the lower MOS transistor Q2 is started before theupper MOS transistor Q1 is switched from the off state to the on stateso as to be reflected on the slope voltage V_(SLP). Accordingly, in thisgeneration example of the slope voltage, the minimum pulse width of theswitched voltage V_(SW) that enables the current feedback can be smallerthan that in the first generation example of the slope voltage describedabove.

Further, in view of stabilizing control system of the current modecontrol, it is preferred to dispose a superimposing portion in the slopecircuit 5, so that the superimposing portion generates a voltage (a newslope voltage V_(SLP′)) in which a sawtooth wave-like or trianglewave-like pseudo slope voltage V_(S) increasing at a constant rateduring the period from the timing t24 to the timing t21 is superimposedon the slope voltage V_(SLP), and to output the new slope voltageV_(SLP′) as the output voltage of the slope circuit 5. In this case, asshown in FIG. 5B, when the slope voltage V_(SLP′) exceeds the errorsignal V_(ERR), the reset signal RESET is switched from low level tohigh level.

<Third Generation Example of Slope Voltage>

Structures of the current sensing circuit 4 and the slope circuit 5 arethe same as those in the first generation example and the secondgeneration example of the slope voltage.

FIG. 6A is a timing chart showing a still another operation example ofthe switching power supply device 101.

In the example shown in FIG. 6A, the timing control circuit 1 switchesthe gate signal G1 from low level to high level when the set signal SETis switched from high level to low level, and switches the gate signalG1 from high level to low level when the reset signal RESET is switchedfrom low level to high level.

In addition, the timing control circuit 1 switches an internal clocksignal CLK from low level to high level when the set signal SET isswitched from low level to high level, on the basis of the set signalSET, so as to generate the internal clock signal CLK having a high levelperiod shorter than a high level period of the set signal SET. Note thateach high level period of the internal clock signal CLK is a constantperiod of time in which the current feedback is performed in the thirdgeneration example of the slope voltage. Note that it is preferred toadjust each high level period of the internal clock signal CLK so thatthe internal clock signal CLK is switched from high level to low levelbefore the dead time starts just after the lower MOS transistor Q2 isswitched from the on state to the off state.

Further, when the internal clock signal CLK is switched from low levelto high level, regardless of a level changing state of the reset signalRESET, the timing control circuit 1 forces the gate signal G1 to be lowlevel and the gate signal G2 to be high level. In this way, when theinternal clock signal CLK is switched from low level to high level, thecurrent feedback can be securely started.

The slope circuit 5 changes on and off of the switches S1 to S3 inaccordance with an instruction from the timing control circuit 1.

When the reset signal RESET is switched from low level to high level (attiming t31), the slope circuit 5 maintains the off state of the switchS1, changes the switch S2 from the off state to the on state, andchanges the switch S3 from the off state to the on state. In this way,the capacitors C2 and C3 are discharged, and each of the charge voltageV_(CRG) of the capacitor C2 and the slope voltage V_(SLP) becomes zero.

Then, the slope circuit 5 changes the switch S2 from the on state to theoff state so as to finish discharging the capacitor C2. After that, theslope circuit 5 changes the switch S1 from the off state to the on statewhen the internal clock signal CLK is switched from low level to highlevel (at timing t32).

Next, when the internal clock signal CLK is switched from high level tolow level (at timing t33), the slope circuit 5 changes the switch S1from the on state to the off state.

During the period from the timing t32 to the timing t33, namely, duringa constant period of time in the high level period of the set signalSET, the switch S1 forms the current path from the voltage currentconversion circuit 4A to the capacitor C2. Accordingly, the voltagecurrent conversion circuit 4A senses the current flowing in the lowerMOS transistor Q2, and the information of the current flowing in thelower MOS transistor Q2 is accumulated in a form of the charge voltageV_(CRG).

After that, the slope circuit 5 changes the switch S3 from the on stateto the off state at timing t34. The timing of t34 can be the starttiming of a dead time just after the lower MOS transistor Q2 is switchedfrom the on state to the off state, for example. Because the outputcurrent of the voltage current conversion circuit 5A charges thecapacitor C3 during the period from the timing t34 to the next timingt31, the information of the current flowing in the lower MOS transistorQ2 during the period from the timing t32 to the timing t33 istransmitted and reflected on the slope voltage V_(SLP).

In the first generation example and the second generation example of theslope voltage described above, because an on period of the switch S1depends on an on period of the upper MOS transistor Q1, the on period ofthe switch S1 varies depending on the ratio of the output voltageV_(OUT) to the input voltage V_(IN) of the switching power supply device101, and hence there is a tendency that the control system of thecurrent mode control becomes unstable. In contrast, in this generationexample of the slope voltage, because the on period of the switch S1 isa constant period, the control system of the current mode control isstabilized.

In addition, in this generation example of the slope voltage, similarlyto the second generation example of the slope voltage described above,the transmission of the information of the current flowing in the lowerMOS transistor Q2 is started before the upper MOS transistor Q1 isswitched from the off state to the on state so as to be reflected on theslope voltage V_(SLP). Accordingly, in this generation example of theslope voltage, the minimum width of the switched voltage V_(SW) thatenables the current feedback can be smaller than that in the firstgeneration example of the slope voltage described above.

Further, although the minimum pulse width of the switched voltage V_(SW)that enables the current feedback is the same as that in the firstgeneration example of the slope voltage described above, it is alsopossible to modify this generation example of the slope voltage in sucha manner that the transmission of the information of the current flowingin the lower MOS transistor Q2 is started so as to be reflected on theslope voltage V_(SLP) when the upper MOS transistor Q1 is switched fromthe off state to the on state.

Further, in view of more stabilizing the control system of the currentmode control, it is preferred to dispose a superimposing portion in theslope circuit 5, so that the superimposing portion generates a voltage(a new slope voltage V_(SLP′)) in which a sawtooth wave-like or trianglewave-like pseudo slope voltage V_(S) increasing at a constant rateduring the period from the timing t34 to the timing t31 is superimposedon the slope voltage V_(SLP), and to output the new slope voltageV_(SLP′) as the output voltage of the slope circuit 5. In this case, asshown in FIG. 6B, when the slope voltage V_(SLP′) exceeds the errorsignal V_(ERR), the reset signal RESET is switched from low level tohigh level.

<Fourth Generation Example of Slope Voltage>

In the first to third generation examples of the slope voltage describedabove, the slope voltage is generated having a slope gradient on whichthe current information is reflected as shown in FIG. 7. In contrast, inthis generation example, the slope voltage is generated having a slopeoffset voltage on which the current information is reflected as shown inFIG. 8.

When adopting the first to third generation examples of the slopevoltage described above, operating conditions are limited becausetransfer characteristics (closed loop transfer function) of the controlsystem depends on the input voltage V_(IN) and output load (that isconnected to the application terminal of the output voltage V_(OUT)). Incontrast, when adopting this generation example, there is a merit thatthe operating conditions are not limited because the transfercharacteristics (closed loop transfer function) of the control system donot depend on the input voltage V_(IN) and the output load.

Hereinafter, a relationship among the transfer characteristics of thecontrol system described above, the input voltage V_(IN), and the outputload is described below in detail.

(Case of Adopting First to Third Generation Examples of the SlopeVoltage)

The relationship of the following equation (1) holds between an on dutyD of the upper MOS transistor Q1 and a value V_(C) of the error signalV_(ERR) output from the error amplifier 2. Note that S_(E) denotes aslope gradient (fixed value) of the pseudo slope voltage V_(S), S_(N)denotes a slope gradient on which the information of the current flowingin the lower MOS transistor Q2 is reflected, and T denotes a coefficientsuch that the maximum value of D becomes one.

$\begin{matrix}\begin{matrix}{D = \frac{V_{C}}{\left( {S_{N} + S_{E}} \right) \cdot T}} \\{= \frac{\left( {S_{N} + S_{E}} \right) \cdot T \cdot \frac{V_{OUT}}{V_{IN}}}{\left( {S_{N} + S_{E}} \right) \cdot T}}\end{matrix} & (1)\end{matrix}$

Here, when the value V_(C) of the error signal V_(ERR) output from theerror amplifier 2 varies by ΔV_(C), the on duty D of the upper MOStransistor Q1 varies by ΔD, and hence the following equation (2) issatisfied. Note that S_(N′) denotes the slope gradient on which theinformation of the current flowing in the lower MOS transistor Q2 isreflected.

$\begin{matrix}\begin{matrix}{{D + {\Delta\; D}} = \frac{V_{C} + {\Delta\; V_{C}}}{\left( {S_{N}^{\prime} + S_{E}} \right) \cdot T}} \\{= \frac{{\left( {S_{N} + S_{E}} \right) \cdot T \cdot \frac{V_{OUT}}{V_{IN}}} + {\Delta\; V_{C}}}{\left( {S_{N}^{\prime} + S_{E}} \right) \cdot T}}\end{matrix} & (2)\end{matrix}$

In accordance with the above-mentioned equation (1) and equation (2), ΔDis expressed by the following equation (3).

$\begin{matrix}{{\Delta\; D} = \frac{{\left( {S_{N} - S_{N}^{\prime}} \right) \cdot T \cdot \frac{V_{OUT}}{V_{IN}}} + {\Delta\; V_{C}}}{\left( {S_{E} + S_{N}^{\prime}} \right) \cdot T}} & (3)\end{matrix}$

Here, because S_(N) is expressed by the following equation (4), thefollowing equation (5) is satisfied. Note that t_(P) denotes theaccumulation time of the information of the current flowing in the lowerMOS transistor Q2, and I_(OUT) denotes the output current supplied tothe output load. When the value V_(C) of the error signal V_(ERR) outputfrom the error amplifier 2 varies by ΔV_(C), the output current I_(OUT)varies by ΔI_(OUT).

$\begin{matrix}{S_{N} = {\int_{0}^{t_{P}}{A\; I_{OUT}d\; t}}} & (4) \\\begin{matrix}{{S_{N}^{\prime} - S_{N}} = {{\int_{0}^{t_{P}}{{A\left( {I_{OUT} + {\Delta\; I}} \right)}d\; t}} - {\int_{0}^{t_{P}}{{AI}_{OUT}d\; t}}}} \\{= {{A \cdot \Delta}\;{I \cdot t_{P}}}}\end{matrix} & (5)\end{matrix}$

Here, ΔI is expressed by the following equation (6), and ΔV_(OUT) isexpressed by the following equation (7). Note that G_(DV(S)) is aparameter for shaping the switched voltage V_(SW) into the outputvoltage V_(OUT).

$\begin{matrix}{{\Delta\; I} = \frac{\Delta\; V_{OUT}}{Z_{OUT}}} & (6) \\{{\Delta\; V_{OUT}} = {{V_{IN} \cdot \Delta}\;{D \cdot G_{{DV}{(S)}}}}} & (7)\end{matrix}$

The above-mentioned equation (6) and equation (7) are substituted intothe above-mentioned equation (3) and equation (5), and the equations areorganized. Then, the following equation (8) is derived.

$\begin{matrix}{\frac{\Delta\; D}{\Delta\; V_{C}} = \frac{1}{{\left( {S_{E} + S_{N}^{\prime}} \right)T} = {\frac{A\;{V_{OUT} \cdot t_{F}}T}{Z_{OUT}}G_{{DV}{(S)}}}}} & (8)\end{matrix}$

Using the above-mentioned equation (8), a ratio of ΔV_(OUT) to ΔV_(C) isexpressed by the following equation (9).

$\begin{matrix}\begin{matrix}{\frac{\Delta\; V_{OUT}}{\Delta\; V_{C}} = {\frac{\Delta\; D}{\Delta\; V_{C}} \cdot \frac{\Delta\; V_{OUT}}{\Delta\; D}}} \\{= \frac{V_{IN} \cdot G_{{DV}{(S)}}}{{\left( {S_{E} + S_{N}^{\prime}} \right)T} + {\frac{{{AV}_{OUT} \cdot t_{F}}T}{Z_{OUT}}G_{{DV}{(S)}}}}} \\{= \frac{V_{IN} \cdot G_{{DV}{(S)}}}{{\left( {S_{E} + S_{N}^{\prime}} \right)T} + {\frac{{S_{N} \cdot V_{OUT}}T}{Z_{OUT} \cdot I_{OUT}}G_{{DV}{(S)}}}}}\end{matrix} & (9)\end{matrix}$

As understood from the above-mentioned equation (9), when the inputvoltage V_(IN) increases, a voltage gain is increased. When the outputcurrent I_(OUT) increases, the G_(DV(S)) of the denominator and thenumerator are hardly cancelled by each other, and hence it becomesdifficult to perform the current feedback. In other words, the transfercharacteristics (closed loop transfer function) of the control systemdepend on the input voltage V_(IN) and the output load.

(Case of Adopting this Generation Example of the Slope Voltage)

Similarly to the case of adopting the first to third generation examplesof the slope voltage, the transfer characteristics of the control systemare considered, and the following equation (12) is derived from thefollowing equation (10). Note that R_(S) denotes a parameter indicatinghow largely the current information is reflected as an offset voltage onthe slope voltage and is expressed by the following equation (11).

$\begin{matrix}{{\Delta\; D} = \frac{{\Delta\; V_{C}} - {{R_{S} \cdot \Delta}\; I}}{S_{E} \cdot T}} & (10) \\{R_{S} = \frac{V_{SLP}}{I_{OUT}}} & (11) \\{\frac{\Delta\; V_{OUT}}{\Delta\; V_{C}} = \frac{V_{IN} \cdot G_{{DV}{(S)}}}{{S_{E} \cdot T} + {\frac{R_{S}}{Z_{OUT}}V_{IN}G_{{DV}{(S)}}}}} & (12)\end{matrix}$

Here, the following equation (14) is satisfied when the condition of thefollowing equation (13) is set.

$\begin{matrix}{{S_{E} \cdot T} ⪡ {\frac{R_{S}}{Z_{OUT}}V_{IN}G_{{DV}{(S)}}}} & (13) \\{\frac{\Delta\; V_{OUT}}{\Delta\; V_{C}} = \frac{Z_{OUT}}{R_{S}}} & (14)\end{matrix}$

As understood from the above-mentioned equation (14), the transfercharacteristics of the control system (closed loop transfer function)does not depend on the input voltage V_(IN) and the output load.

(Details of this Generation Example)

Next, details of this generation example are described. The currentsensing circuit 4 and the slope circuit 5 have the structure shown inFIG. 9, and the switching power supply device 101 operates as shown inFIG. 10.

In the example shown in FIG. 9, the current sensing circuit 4 isconstituted of the voltage current conversion circuit 4A. In addition,in the example shown in FIG. 9, the slope circuit 5 is constituted ofswitches S1, S2, and S4, the capacitor C2, and the constant currentsource 9. Note that it is preferred that a value of the constant currentoutput from the constant current source 9 be adjustable.

Each of the voltage current conversion circuit 4A and the constantcurrent source 9 is a circuit driven by the internal source voltageV_(CC) generated in an integrated circuit (IC) including the timingcontrol circuit 1, the error amplifier 2, the reference voltage source3, the current sensing circuit 4, the slope circuit 5, the comparator 6,and the oscillator 7.

The voltage current conversion circuit 4A converts the drain-sourcevoltage of the lower MOS transistor Q2 into current and outputs thecurrent. When the switch S1 is on, the capacitor C2 is charged by theoutput current of the voltage current conversion circuit 4A. When theswitch S4 is on, the capacitor C2 is charged by the output current ofthe constant current source 9. On the other hand, when the switch S2 ison, the capacitor C2 is discharged. The charge voltage of the capacitorC2 becomes the slope voltage V_(SLP).

In the example shown in FIG. 10, the timing control circuit 1 switchesthe gate signal G1 from low level to high level when the set signal SETis switched from high level to low level, and switches the gate signalG1 from high level to low level when the reset signal RESET is switchedfrom low level to high level.

In addition, the timing control circuit 1 is switched the internal clocksignal CLK from low level to high level when the set signal SET isswitched from low level to high level on the basis of the set signalSET, so as to generate the internal clock signal CLK having a high levelperiod shorter than the high level period of the set signal SET. Notethat each high level period of the internal clock signal CLK is aconstant period of time during which the current feedback is performedin the fourth generation example of the slope voltage. Note that eachhigh level period of the internal clock signal CLK should be adjusted sothat the internal clock signal CLK is switched from high level to lowlevel before the dead time starts just after the lower MOS transistor Q2is switched from the on state to the off state.

Further, when the internal clock signal CLK is switched from low levelto high level, regardless of a level changing state of the reset signalRESET, the timing control circuit 1 forces the gate signal G1 to be lowlevel and the gate signal G2 to be high level. In this way, when theinternal clock signal CLK is switched from low level to high level, thecurrent feedback can be securely started.

The slope circuit 5 changes on and off of the switches S1, S2, and S4 inaccordance with an instruction from the timing control circuit 1.

When the reset signal RESET is switched from low level to high level (attiming t41), the slope circuit 5 maintains the off state of the switchS1, changes the switch S2 from the off state to the on state, andchanges the switch S4 from the on state to the off state. In this way,the capacitor C2 is discharged, and the slope voltage V_(SLP) as thecharge voltage of the capacitor C2 becomes zero.

Then, the slope circuit 5 changes the switch S2 from the on state to theoff state so as to finish discharging the capacitor C2. After that, theslope circuit 5 changes the switch S1 from the off state to the on statewhen the internal clock signal CLK is switched from low level to highlevel (at timing t42).

Next, when the internal clock signal CLK is switched from high level tolow level (at timing t43), the slope circuit 5 changes the switch S1from the on state to the off state.

During the period from the timing t42 to the timing t43, the switch S1forms the current path from the voltage current conversion circuit 4A tothe capacitor C2. Accordingly, the information of the current flowing inthe lower MOS transistor Q2 is accumulated in a form of the chargevoltage of the capacitor C2.

Next, when the set signal SET is switched from high level to low level(at timing t44), the slope circuit 5 changes the switch S4 from the offstate to the on state. During the period from the timing t44 to the nexttiming t41, the output current of the constant current source 9 chargesthe capacitor C2. In this way, the slope voltage V_(SLP) as the chargevoltage of the capacitor C2 becomes a voltage in which a voltageincreasing at a constant ratio corresponding to the output current ofthe constant current source 9 (a gradient corresponding to the outputcurrent of the constant current source 9) is superimposed on the offsetvoltage on which the information of the current flowing in the lower MOStransistor Q2 is reflected. Further, the slope voltage V_(SLP) as thecharge voltage of the capacitor C2 becomes an output signal of the slopecircuit 5.

In this generation example, the slope voltage V_(SLP) having the slopeoffset voltage on which the information of the current flowing in thelower MOS transistor Q2 is reflected is generated. Accordingly, thetransfer characteristics (closed loop transfer function) of the controlsystem do not depend on the input voltage V_(IN) and the output load.Accordingly, the operating condition of the switching power supplydevice 101 is not limited.

In addition, in this generation example, similarly to the secondgeneration example of the slope voltage described above, thetransmission of the information of the current flowing in the lower MOStransistor Q2 is started before the upper MOS transistor Q1 is switchedfrom the off state to the on state so as to be reflected on the slopevoltage V_(SLP). Accordingly, in this generation example of the slopevoltage, the minimum pulse width of the switched voltage V_(SW) thatenables the current feedback can be smaller than that of the firstgeneration example of the slope voltage described above.

In addition, in this generation example, similarly to the thirdgeneration example of the slope voltage described above, the on periodof the switch S1 is a constant period of time. Accordingly, the controlsystem of the current mode control is stabilized.

General Structure (Second Embodiment)

FIG. 11 is a diagram showing an example of a general structure of asecond embodiment of the current mode control type switching powersupply device. A switching power supply device 102 of this structuralexample has a structure in which a current sensing circuit 10 is addedto the switching power supply device 101.

The current sensing circuit 10 senses the current flowing in the upperMOS transistor Q1 on the basis of the drain-source voltage in the onstate of the upper MOS transistor Q1, namely the voltage between bothends of the on resistance of the upper MOS transistor Q1.

As described above in the first embodiment, the slope circuit 5generates and outputs the slope voltage corresponding to the currentflowing in the lower MOS transistor Q2 sensed by the current sensingcircuit 4. In this way, even if the ratio of the output voltage V_(OUT)to the input voltage V_(IN) is small (even if the switched voltageV_(SW) has a small pulse width), the current feedback can be performed.However, in the form in which the slope circuit 5 generates and outputsthe slope voltage corresponding to the current flowing in the lower MOStransistor Q2 sensed by the current sensing circuit 4, when the pulsewidth of the switched voltage V_(SW) becomes large, the period of timeduring which the current flowing in the lower MOS transistor Q2 can besensed (while the lower MOS transistor Q2 is on) is decreased, and hencethe current feedback may not be performed. In contrast, in the form inwhich the slope voltage corresponding to the current flowing in theupper MOS transistor Q1 is generated so as to perform the current modecontrol like the conventional technique, when the pulse width of theswitched voltage V_(SW) becomes large, the period of time during whichthe current flowing in the upper MOS transistor Q1 can be sensed (aperiod of time while the upper MOS transistor Q1 is on) is increased,and hence there is no possibility that the current feedback cannot beperformed.

Thus, in accordance with an instruction from the timing control circuit1, the slope circuit 5 of this embodiment generates and outputs theslope voltage corresponding to the current flowing in the lower MOStransistor Q2 sensed by the current sensing circuit 4 if the ratio ofthe output voltage to the input voltage (V_(OUT)/V_(IN)) of theswitching power supply device 102 is 50% or less, while it generates andoutputs the slope voltage corresponding to the current flowing in theupper MOS transistor Q1 sensed by the current sensing circuit 10 ifV_(OUT)/V_(IN) is more than 50%. In this way, the current feedback canbe performed not only in the case where the pulse width of the switchedvoltage V_(SW) is decreased but also in the case where the pulse widthof the switched voltage V_(SW) is increased.

The generation of the slope voltage corresponding to the current flowingin the lower MOS transistor Q2 sensed by the current sensing circuit 4should be the same as that in each of the generation examples describedabove in the first embodiment, for example. In addition, the generationof the slope voltage corresponding to the current flowing in the upperMOS transistor Q1 sensed by the current sensing circuit 10 is knowntechnique, and description thereof is omitted.

FIG. 12A is a timing chart showing an example of determination whetheror not V_(OUT)/V_(IN) is 50% or less. This determination is performed bythe timing control circuit 1 that switches the gate signal G1 from lowlevel to high level when the set signal SET is switched from low levelto high level and switches the gate signal G1 from high level to lowlevel when the reset signal RESET is switched from low level to highlevel.

The timing control circuit 1 generates a divided clock signal DIV basedon the set signal SET. The divided clock signal DIV is a half-dividedsignal of the set signal SET in which the switch timing from low levelto high level is the same as that of the set signal SET.

In addition, the timing control circuit 1 generates a sense clock signalDET based on the set signal SET and the divided clock signal DIV. Thesense clock signal DET has the same switch timing from low level to highlevel as the set signal SET and the divided clock signal DIV, and isswitched from high level to low level at timing when the divided clocksignal DIV is switched from low level to high level and the set signalSET is not switched from low level to high level.

Further, the timing control circuit 1 determines that the V_(OUT)/V_(IN)is more than 50% if the gate signal G1 is high level when the senseclock signal DET is switched from high level to low level (in this case,the switched voltage V_(SW) is high level), and determines that theV_(OUT)/V_(IN) is 50% or less if the gate signal G1 is low level whenthe sense clock signal DET is switched from high level to low level (inthis case, the switched voltage V_(SW) is low level).

FIG. 12B is a timing chart showing another example of determinationwhether or not V_(OUT)/V_(IN) is 50% or less. This determination isperformed by the timing control circuit 1 that switches the gate signalG1 from low level to high level when the set signal SET is switched fromhigh level to low level, and switches the gate signal G1 from high levelto low level when the reset signal RESET is switched from low level tohigh level.

The timing control circuit 1 generates the divided clock signal DIVbased on the set signal SET. The divided clock signal DIV is ahalf-divided signal of the set signal SET and has the same switch timingfrom high level to low level as the set signal SET.

In addition, the timing control circuit 1 generates the sense clocksignal DET based on the set signal SET and the divided clock signal DIV.The sense clock signal DET has the switch timing from low level to highlevel that is the same as the switch timing of the set signal SET andthe divided clock signal DIV from high level to low level, and isswitched from high level to low level at timing when the divided clocksignal DIV is switched from high level to low level and the set signalSET is not switched from high level to low level.

Further, the timing control circuit 1 determines that V_(OUT)/V_(IN) ismore than 50% if the gate signal G1 is high level when the sense clocksignal DET is switched from high level to low level (in this case, theswitched voltage V_(SW) is high level), and determines thatV_(OUT)/V_(IN) is 50% or less if the gate signal G1 is low level whenthe sense clock signal DET is switched from high level to low level (inthis case, the switched voltage V_(SW) is low level).

In the above description, the slope circuit 5 outputs the slope voltagecorresponding to the current flowing in the lower MOS transistor Q2sensed by the current sensing circuit 4 if V_(OUT)/V_(IN) is 50% orless. However, 50% is merely an example, and another value may beadopted.

Further in the above description, the slope circuit 5 outputs the slopevoltage corresponding to the current flowing in the upper MOS transistorQ1 sensed by the current sensing circuit 10 if V_(OUT)/V_(IN) is morethan 50%. It is possible not to perform the current mode control ifV_(OUT)/V_(IN) is more than a predetermined value so as to avoid thatthe current feedback cannot be performed when the pulse width of theswitched voltage V_(SW) is increased. For instance, it is possible toadopt the following structure. The slope circuit 5 generates the pseudoslope voltage. If V_(OUT)/V_(IN) is the predetermined value or smaller,the slope circuit 5 outputs a voltage in which the pseudo slope voltageis superimposed on the slope voltage corresponding to the currentflowing in the lower MOS transistor Q2 sensed by the current sensingcircuit 4 (a new slope voltage) as the output voltage of the slopecircuit 5. If V_(OUT)/V_(IN) is larger than the predetermined value, theslope circuit 5 outputs the pseudo slope voltage as the output voltageof the slope circuit 5.

<Applications>

Next, there is described an application example of the switching powersupply device 101 described above. FIG. 13 is an outside view showing astructural example of a vehicle in which in-vehicle equipment ismounted. A vehicle X of this structural example includes in-vehicleequipment X11 to X17 and a battery (not shown) configured to supplyelectric power to the in-vehicle equipment X11 to X17.

The in-vehicle equipment X11 is an engine control unit configured toperform control related to engine (such as injection control, electronicthrottle control, idling control, oxygen sensor heater control, andautomatic cruise control).

The in-vehicle equipment X12 is a lamp control unit configured tocontrol on and off of a high intensity discharged lamp (HID), a daytimerunning lamp (DRL) and the like.

The in-vehicle equipment X13 is a transmission control unit configuredto perform control related to transmission.

The in-vehicle equipment X14 is a body control unit configured toperform control related to movement of the vehicle X (such as anti-lockbrake system (ABS) control, electric power steering (EPS) control, andelectronic suspension control).

The in-vehicle equipment X15 is a security control unit configured toperform control for driving a door lock, an anti-theft alarm, and thelike.

The in-vehicle equipment X16 is electronic equipment mounted in thevehicle X before shipping, as standard equipment or manufactureroptional equipment, such as wipers, electric door mirrors, powerwindows, electric sunroof, an electric sheet, and an air conditioner.

The in-vehicle equipment X17 is electronic equipment mounted in thevehicle X by user's intention, such as in-vehicle audio/visual (A/V)equipment, a car navigation system, and an electronic toll collection(ETC) system.

Note that the switching power supply device 101 described above can beincorporated in any one of the in-vehicle equipment X11 to X17 describedabove.

Another Variation Example

Note that the structure of the present invention can be variouslymodified from the embodiment described above within the scope of theinvention without deviating from the spirit thereof.

For instance, the step-down type switching power supply device isexemplified in the embodiment described above, but applications of thepresent invention are not limited to this. The present invention can beapplied also to a step-up/down type switching power supply device thatcan perform not only the step down operation but also a step upoperation.

In this way, the embodiment described above is merely an example inevery aspect and should not be interpreted as a limitation. Thetechnical scope of the present invention should be defined not by thedescription of the embodiment described above but by the claims, whichshould be interpreted to include all modifications belonging to meaningsand ranges equivalent to the claims.

<Summary>

(First Technical Feature)

Among the current mode control type switching power supply devicesdescribed above, the current mode control type switching power supplydevice having the first technical feature includes the first switchhaving the first terminal connected to the first application terminal towhich the input voltage is applied, the second switch having the firstterminal connected to the second terminal of the first switch and thesecond terminal connected to the second application terminal to which apredetermined voltage lower than the input voltage is applied, thecurrent sensing portion configured to sense current flowing in thesecond switch, and the controller configured to control the first switchand the second switch in accordance with the current sensed by thecurrent sensing portion. The controller includes an accumulating portionconfigured to accumulate information of the current sensed by thecurrent sensing portion during a predetermined period of time while thefirst switch is in the off state, and a reflecting portion configured tostart transmission of the current information accumulated by theaccumulating portion before the first switch is changed from the offstate to the on state so as to reflect the current informationaccumulated by the accumulating portion on the slope voltage, andcontrols the first switch and the second switch in accordance with theslope voltage (Structure 1-1).

In addition, in the current mode control type switching power supplydevice having Structure 1-1 described above, the accumulating portionand the reflecting portion may be circuits driven by the same sourcevoltage (Structure 1-2).

In addition, in the current mode control type switching power supplydevice having Structure 1-1 or Structure 1-2, the current sensingportion may be the voltage current conversion circuit configured toconvert the voltage corresponding to the current flowing in the secondswitch into current, the accumulating portion may include the capacitorto be charged by the output current of the voltage current conversioncircuit, and the reflecting portion may reflect the charge voltage ofthe capacitor on the slope voltage (Structure 1-3).

In addition, in the current mode control type switching power supplydevice having Structure 1-3 described above, the accumulating portionmay further include a charging switch configured to make and break thecurrent path from the output terminal of the voltage current conversioncircuit to the capacitor (Structure 1-4).

In addition, in the current mode control type switching power supplydevice having Structure 1-4 described above, the accumulating portionmay change the charging switch from the off state to the on state at theend timing of the dead time just after the first switch is changed fromthe on state to the off state, and may change the charging switch fromthe on state to the off state at a start timing of a dead time justafter the second switch is changed from the on state to the off state(Structure 1-5).

In addition, in the current mode control type switching power supplydevice having any one of Structures 1-3 to 1-5 described above, theaccumulating portion may have a resetting portion configured todischarge the capacitor so as to reset the charge voltage of thecapacitor (Structure 1-6).

In addition, in the current mode control type switching power supplydevice having any one of Structures 1-1 to 1-6 described above, thecontroller may include the error amplifier configured to generate anerror signal corresponding to a difference between a voltagecorresponding to the output voltage of the current mode control typeswitching power supply device and a reference voltage, the comparatorconfigured to compare the slope voltage with the error signal so as togenerate the reset signal as the comparison signal, the oscillatorconfigured to generate the set signal as the clock signal of apredetermined frequency, and the timing control circuit configured tocontrol on and off of the first switch and on and off of the secondswitch in accordance with the set signal and the reset signal (Structure1-7).

In addition, in the current mode control type switching power supplydevice having any one of Structures 1-1 to 1-7 described above, thesecond switch may be a MOS transistor, and the current sensing portionmay sense the current flowing in the second switch by using a voltagebetween both ends of the on resistor of the MOS transistor (Structure1-8).

In addition, among the in-vehicle equipment disclosed in thisspecification, the in-vehicle equipment having the first technicalfeature includes the current mode control type switching power supplydevice having any one of Structures 1-1 to 1-8 (Structure 1-9).

In addition, among the vehicles disclosed in this specification, thevehicle having the first technical feature includes the in-vehicleequipment having Structure 1-9 and a battery configured to supplyelectric power to the in-vehicle equipment (Structure 1-10).

(Second Technical Feature)

Among the current mode control type switching power supply devicesdescribed above, the current mode control type switching power supplydevice having the second technical feature includes the first switchhaving the first terminal connected to the first application terminal towhich the input voltage is applied, the second switch having the firstterminal connected to the second terminal of the first switch and thesecond terminal connected to the second application terminal to which apredetermined voltage lower than the input voltage is applied, thecurrent sensing portion configured to sense current flowing in thesecond switch, and the controller configured to control the first switchand the second switch in accordance with the current sensed by thecurrent sensing portion. The controller includes a slope voltagegenerating portion configured to accumulate information of the currentsensed by the current sensing portion during a predetermined period oftime while the first switch is in the off state so as to generate theslope voltage based on the accumulated current information, and controlsthe first switch and the second switch in accordance with the slopevoltage (Structure 2-1).

In addition, in the current mode control type switching power supplydevice having Structure 2-1 described above, the current sensing portionmay be the voltage current conversion circuit configured to convert thevoltage corresponding to the current flowing in the second switch intocurrent, and the slope voltage generating portion may include thecapacitor to be charged by the output current of the voltage currentconversion circuit (Structure 2-2).

In addition, in the current mode control type switching power supplydevice having Structure 2-2 described above, the slope voltagegenerating portion may further include a charging switch configured tomake and break the current path from the output terminal of the voltagecurrent conversion circuit to the capacitor (Structure 2-3).

In addition, in the current mode control type switching power supplydevice having Structure 2-2 or 2-3 described above, the slope voltagegenerating portion may include the resetting portion configured todischarge the capacitor so as to reset the charge voltage of thecapacitor (Structure 2-4).

In addition, in the current mode control type switching power supplydevice having any one of Structures 2-1 to 2-4 described above, thecontroller may include the error amplifier configured to generate theerror signal corresponding to the difference between the voltagecorresponding to the output voltage of the current mode control typeswitching power supply device and the reference voltage, the comparatorconfigured to compare the slope voltage with the error signal so as togenerate the reset signal as the comparison signal, the oscillatorconfigured to generate the set signal as the clock signal of thepredetermined frequency, and the timing control circuit configured tocontrol on and off of the first switch and on and off of the secondswitch in accordance with the set signal and the reset signal (Structure2-5).

In addition, in the current mode control type switching power supplydevice having any one of Structures 2-1 to 2-5, the second switch may bea MOS transistor, and the current sensing portion may sense the currentflowing in the second switch by using the voltage between both ends ofthe on resistor of the MOS transistor (Structure 2-6).

In addition, among the in-vehicle equipment disclosed in thisspecification, the in-vehicle equipment having the second technicalfeature includes the current mode control type switching power supplydevice having any one of Structures 2-1 to 2-6 (Structure 2-7).

In addition, among the vehicles disclosed in this specification, thevehicle having the second technical feature includes the in-vehicleequipment having Structure 2-7 and a battery configured to supplyelectric power to the in-vehicle equipment (Structure 2-8).

(Third Technical Feature)

Among the current mode control type switching power supply devicesdescribed above, the current mode control type switching power supplydevice having the third technical feature includes the first switchhaving the first terminal connected to the first application terminal towhich the input voltage is applied, the second switch having the firstterminal connected to the second terminal of the first switch and thesecond terminal connected to the second application terminal to which apredetermined voltage lower than the input voltage is applied, thecurrent sensing portion configured to sense current flowing in thesecond switch, and the controller configured to control the first switchand the second switch in accordance with the current sensed by thecurrent sensing portion. The controller includes the accumulatingportion configured to accumulate information of the current sensed bythe current sensing portion during a constant period of time while thefirst switch is in the off state, and the reflecting portion configuredto reflect the current information accumulated by the accumulatingportion on the slope voltage, and controls the first switch and thesecond switch in accordance with the slope voltage (Structure 3-1).

In addition, in the current mode control type switching power supplydevice having Structure 3-1 described above, the controller includes theerror amplifier configured to generate the error signal corresponding toa difference between the voltage corresponding to the output voltage ofthe current mode control type switching power supply device and thereference voltage, the comparator configured to compare the slopevoltage with the error signal so as to generate the reset signal as thecomparison signal, the oscillator configured to generate the set signalas the clock signal of a predetermined frequency, and the timing controlcircuit configured to control on and off of the first switch and on andoff of the second switch in accordance with the set signal and the resetsignal, and the constant period of time is set in the high level periodof the set signal (Structure 3-2).

In addition, in the current mode control type switching power supplydevice having Structure 3-2 described above, the timing control circuitturns on the first switch when the set signal is switched from highlevel to low level, turns off the first switch when the reset signal isswitched from low level to high level, and forcibly turns off the firstswitch and turns on the second switch regardless of the level changingstate of the reset signal when the set signal is switched from low levelto high level (Structure 3-3).

In addition, in the current mode control type switching power supplydevice having any one of Structures 3-1 to 3-3 described above, theaccumulating portion and the reflecting portion may be circuits drivenby the same source voltage (Structure 3-4).

In addition, in the current mode control type switching power supplydevice having any one of Structures 3-1 to 3-4 described above, thecurrent sensing portion may be the voltage current conversion circuitconfigured to convert the voltage corresponding to the current flowingin the second switch into current, the accumulating portion may includethe capacitor to be charged by the output current of the voltage currentconversion circuit, and the reflecting portion reflects the chargevoltage of the capacitor on the slope voltage (Structure 3-5).

In addition, in the current mode control type switching power supplydevice having Structure 3-5 described above, the accumulating portionmay further include the charging switch configured to make and break thecurrent path from the output terminal of the voltage current conversioncircuit to the capacitor (Structure 3-6).

In addition, in the current mode control type switching power supplydevice having Structure 3-5 or 3-6 described above, the accumulatingportion may include the resetting portion configured to discharge thecapacitor so as to reset the charge voltage of the capacitor (Structure3-7).

In addition, in the current mode control type switching power supplydevice having any one of Structures 3-1 to 3-7 described above, thereflecting portion may start the transmission of the current informationaccumulated by the accumulating portion before the first switch ischanged from the off state to the on state so as to reflect the currentinformation accumulated by the accumulating portion on the slope voltage(Structure 3-8).

In addition, in the current mode control type switching power supplydevice having any one of Structures 3-1 to 3-8 described above, thesecond switch may be a MOS transistor, and the current sensing portionmay sense the current flowing in the second switch by using the voltagebetween both ends of the on resistor of the MOS transistor (Structure3-9).

In addition, among the in-vehicle equipment disclosed in thisspecification, the in-vehicle equipment having the third technicalfeature may include the current mode control type switching power supplydevice having any one of Structures 3-1 to 3-9 (Structure 3-10).

In addition, among the vehicles disclosed in this specification, thevehicle having the third technical feature may include the in-vehicleequipment of Structure 3-10 and a battery configured to supply electricpower to the in-vehicle equipment (Structure 3-11).

(Fourth Technical Feature)

Among the current mode control type switching power supply devicesdescribed above, the current mode control type switching power supplydevice having the fourth technical feature includes the first switchhaving the first terminal connected to the first application terminal towhich the input voltage is applied, the second switch having the firstterminal connected to the second terminal of the first switch and thesecond terminal connected to the second application terminal to which apredetermined voltage lower than the input voltage is applied, thecurrent sensing portion configured to sense current flowing in thesecond switch, and the controller configured to control the first switchand the second switch in accordance with the current sensed by thecurrent sensing portion. The controller includes the accumulatingportion configured to accumulate information of the current sensed bythe current sensing portion during a predetermined period of time whilethe first switch is in the off state, the reflecting portion configuredto reflect the current information accumulated by the accumulatingportion on the offset voltage of the slope voltage, and a gradientsetting portion configured to set the slope gradient of the slopevoltage to a constant value, and controls the first switch and thesecond switch in accordance with the slope voltage (Structures 4-1).

In addition, in the current mode control type switching power supplydevice having Structure 4-1 described above, the predetermined period oftime may be a constant period of time (Structures 4-2).

In addition, in the current mode control type switching power supplydevice having Structure 4-1 or 4-2 described above, the reflectingportion may start the transmission of the current informationaccumulated by the accumulating portion before the first switch ischanged from the off state to the on state so as to reflect the currentinformation accumulated by the accumulating portion on the offsetvoltage of the slope voltage (Structures 4-3).

In addition, in the current mode control type switching power supplydevice having any one of Structures 4-1 to 4-3 described above, thecurrent sensing portion may be the voltage current conversion circuitconfigured to convert the voltage corresponding to the current flowingin the second switch into current, and the accumulating portion and thereflecting portion share the capacitor to be charged by the outputcurrent of the voltage current conversion circuit (Structures 4-4).

In addition, in the current mode control type switching power supplydevice having Structure 4-4 described above, the gradient settingportion may include the constant current source, and a switch for theslope configured to make and break the current path from the constantcurrent source to the capacitor (Structures 4-5).

In addition, in the current mode control type switching power supplydevice having Structure 4-4 or 4-5 described above, the accumulatingportion may further include the charging switch configured to make andbreak the current path from the output terminal of the voltage currentconversion circuit to the capacitor (Structures 4-6).

In addition, in the current mode control type switching power supplydevice having any one of Structures 4-4 to 4-6 described above, theaccumulating portion may include the resetting portion configured todischarge the capacitor so as to reset the charge voltage of thecapacitor (Structures 4-7).

In addition, in the current mode control type switching power supplydevice having any one of Structures 4-1 to 4-7 described above, thecontroller may include the error amplifier configured to generate theerror signal corresponding to the difference between the voltagecorresponding to the output voltage and the reference voltage, thecomparator configured to compare the slope voltage with the error signalso as to generate the reset signal as the comparison signal, theoscillator configured to generate the set signal as the clock signal ofa predetermined frequency, and the timing control circuit configured tocontrol on and off of the first switch and on and off of the secondswitch in accordance with the set signal and the reset signal(Structures 4-8).

In addition, in the current mode control type switching power supplydevice having any one of Structures 4-1 to 4-8 described above, thesecond switch is a MOS transistor, the current sensing portion sensesthe current flowing in the second switch by using the voltage betweenboth ends of the on resistor of the MOS transistor (Structures 4-9).

In addition, among the in-vehicle equipment disclosed in thisspecification, the in-vehicle equipment having the fourth technicalfeature includes the current mode control type switching power supplydevice having any one of Structures 4-1 to 4-9 (Structure 4-10).

In addition, among the vehicles disclosed in this specification, thevehicle having the fourth technical feature includes the in-vehicleequipment having Structure 4-10 and a battery configured to supplyelectric power to the in-vehicle equipment (Structure 4-11).

(Fifth Technical Feature)

Among the current mode control type switching power supply devicesdescribed above, the current mode control type switching power supplydevice having the fifth technical feature includes the first switchhaving the first terminal connected to the first application terminal towhich the input voltage is applied, the second switch having the firstterminal connected to the second terminal of the first switch and thesecond terminal connected to the second application terminal to which apredetermined voltage lower than the input voltage is applied, thecurrent sensing portion configured to sense current flowing in thesecond switch, and the controller configured to control the first switchand the second switch. If the ratio of the output voltage to the inputvoltage is a predetermined value or lower, the controller controls thefirst switch and the second switch in accordance with the current sensedby the current sensing portion. If the ratio of the output voltage tothe input voltage is higher than the predetermined value, the controllercontrols the first switch and the second switch independently of thecurrent sensed by the current sensing portion (Structure 5-1).

In addition, the current mode control type switching power supply devicehaving Structure 5-1 described above may further include a currentsensing portion for the first switch configured to sense current flowingin the first switch, and the controller may control the first switch andthe second switch in accordance with the current sensed by the currentsensing portion for the first switch if the ratio of the output voltageto the input voltage is higher than the predetermined value (Structure5-2).

In addition, in the current mode control type switching power supplydevice having Structure 5-1 or 5-2 described above, the controller mayinclude the slope voltage generating portion configured to accumulateinformation of the current sensed by the current sensing portion duringa predetermined period of time while the first switch is in the offstate so as to generate the slope voltage based on the accumulatedcurrent information if the ratio of the output voltage to the inputvoltage is a predetermined value or lower, and may control the firstswitch and the second switch in accordance with the slope voltage if theratio of the output voltage to the input voltage is a predeterminedvalue or lower (Structure 5-3).

In addition, in the current mode control type switching power supplydevice having Structure 5-3 described above, the current sensing portionmay be the voltage current conversion circuit configured to convert thevoltage corresponding to the current flowing in the second switch intocurrent, and the slope voltage generating portion may include thecapacitor to be charged by the output current of the voltage currentconversion circuit (Structure 5-4).

In addition, in the current mode control type switching power supplydevice having Structure 5-4 described above, the slope voltagegenerating portion may further include the charging switch configured tomake and break the current path from the output terminal of the voltagecurrent conversion circuit to the capacitor (Structure 5-5).

In addition, in the current mode control type switching power supplydevice having Structure 5-4 or 5-5 described above, the slope voltagegenerating portion may include the resetting portion configured todischarge the capacitor so as to reset the charge voltage of thecapacitor (Structure 5-6).

In addition, in the current mode control type switching power supplydevice having any one of Structures 5-3 to 5-6 described above, thecontroller may include the error amplifier configured to generate theerror signal corresponding to the difference between the voltagecorresponding to the output voltage and the reference voltage, thecomparator configured to compare the slope voltage with the error signalso as to generate the reset signal as the comparison signal, theoscillator configured to generate the set signal as the clock signal ofa predetermined frequency, and the timing control circuit configured tocontrol on and off of the first switch and on and off of the secondswitch in accordance with the set signal and the reset signal (Structure5-7).

In addition, in the current mode control type switching power supplydevice having any one of Structures 5-1 to 5-7 described above, thesecond switch may be a MOS transistor, and the current sensing portionmay sense the current flowing in the second switch by using the voltagebetween both ends of the on resistor of the MOS transistor (Structure5-8).

In addition, among the in-vehicle equipment disclosed in thisspecification, the in-vehicle equipment having the fifth technicalfeature includes the current mode control type switching power supplydevice having any one of Structures 5-1 to 5-8 (Structure 5-9).

In addition, among the vehicles disclosed in this specification, thevehicle having the fifth technical feature includes the in-vehicleequipment having Structure 5-9 and a battery configured to supplyelectric power to the in-vehicle equipment (Structure 5-10).

INDUSTRIAL APPLICABILITY

The present invention can be used for current mode control typeswitching power supply devices used in various fields (such as homeappliances, automobiles, and industrial machines).

What is claimed is:
 1. In-vehicle equipment comprising a current mode control type switching power supply device, the current mode control type switching power supply device comprising: a first switch having a first terminal connected to a first application terminal to which an input voltage is applied; a second switch having a first terminal connected to a second terminal of the first switch and a second terminal connected to a second application terminal to which a predetermined voltage lower than the input voltage is applied; a current sensing portion configured to sense current flowing between the first terminal and the second terminal of the second switch; and a controller configured to control the first switch and the second switch in accordance with the current sensed by the current sensing portion, wherein the controller includes an accumulating portion configured to accumulate current information sensed by the current sensing portion during a predetermined period of time while the first switch is in the off state, and a reflecting portion configured to start transmission of the current information accumulated by the accumulating portion before the first switch is changed from the off state to the on state so as to reflect the current information accumulated by the accumulating portion on a slope voltage, and the controller controls the first switch and the second switch in accordance with the slope voltage.
 2. A vehicle comprising: the in-vehicle equipment according to claim 1; and a battery configured to supply electric power to the in-vehicle equipment.
 3. In-vehicle equipment comprising a current mode control type switching power supply device, the current mode control type switching power supply device comprising: a first switch having a first terminal connected to a first application terminal to which an input voltage is applied; a second switch having a first terminal connected to a second terminal of the first switch and a second terminal connected to a second application terminal to which a predetermined voltage lower than the input voltage is applied; a current sensing portion configured to sense current flowing between the first terminal and the second terminal of the second switch; and a controller configured to control the first switch and the second switch in accordance with the current sensed by the current sensing portion, wherein the controller includes a slope voltage generating portion configured to accumulate information of the current sensed by the current sensing portion during a predetermined period of time while the first switch is in the off state so as to generate a slope voltage based on the accumulated current information, and controls the first switch and the second switch in accordance with the slope voltage.
 4. A vehicle comprising: the in-vehicle equipment according to claim 3; and a battery configured to supply electric power to the in-vehicle equipment.
 5. In-vehicle equipment comprising a current mode control type switching power supply device, the current mode control type switching power supply device comprising: a first switch having a first terminal connected to a first application terminal to which an input voltage is applied; a second switch having a first terminal connected to a second terminal of the first switch and a second terminal connected to a second application terminal to which a predetermined voltage lower than the input voltage is applied; a current sensing portion configured to sense current flowing between the first terminal and the second terminal of the second switch; and a controller configured to control the first switch and the second switch in accordance with the current sensed by the current sensing portion, wherein the controller includes an accumulating portion configured to accumulate information of the current sensed by the current sensing portion during a constant period of time while the first switch is in the off state, and a reflecting portion configured to reflect the current information accumulated by the accumulating portion on the slope voltage, and the controller controls the first switch and the second switch in accordance with the slope voltage.
 6. A vehicle comprising: the in-vehicle equipment according to claim 5; and a battery configured to supply electric power to the in-vehicle equipment.
 7. In-vehicle equipment comprising a current mode control type switching power supply device, the current mode control type switching power supply device comprising: a first switch having a first terminal connected to a first application terminal to which an input voltage is applied; a second switch having a first terminal connected to a second terminal of the first switch and a second terminal connected to a second application terminal to which a predetermined voltage lower than the input voltage is applied; a current sensing portion configured to sense current flowing between the first terminal and the second terminal of the second switch; and a controller configured to control the first switch and the second switch in accordance with the current sensed by the current sensing portion, wherein the controller includes an error amplifier configured to amplify an error between a voltage corresponding to an output voltage of the current mode control type switching power supply device and a reference voltage, and the controller controls the first switch by comparing a slope voltage based on the current sensed by the current sensing portion with an output voltage of the error amplifier.
 8. A vehicle comprising: the in-vehicle equipment according to claim 7; and a battery configured to supply electric power to the in-vehicle equipment.
 9. In-vehicle equipment comprising a current mode control type switching power supply device, the current mode control type switching power supply device comprising: a first switch having a first terminal connected to a first application terminal to which an input voltage is applied; a diode having a first terminal connected to a second terminal of the first switch and a second terminal connected to a second application terminal to which a predetermined voltage lower than the input voltage is applied; a current sensing portion configured to sense current flowing in the diode; and a controller configured to control the first switch in accordance with the current sensed by the current sensing portion, wherein the controller includes an error amplifier configured to amplify an error between a voltage corresponding to an output voltage of the current mode control type switching power supply device and a reference voltage, and the controller controls the first switch by comparing a slope voltage based on the current sensed by the current sensing portion with an output voltage of the error amplifier.
 10. A vehicle comprising: the in-vehicle equipment according to claim 9; and a battery configured to supply electric power to the in-vehicle equipment.
 11. The in-vehicle equipment according to claim 1, wherein the accumulating portion and the reflecting portion are circuits driven by the same source voltage.
 12. The in-vehicle equipment according to claim 1, wherein the current sensing portion is a voltage current conversion circuit configured to convert the voltage corresponding to the current flowing in the second switch into current, the accumulating portion includes a capacitor to be charged by an output current of the voltage current conversion circuit, and the reflecting portion reflects a charge voltage of the capacitor on the slope voltage.
 13. The in-vehicle equipment according to claim 12, wherein the accumulating portion further includes a charging switch configured to make and break a current path from an output terminal of the voltage current conversion circuit to the capacitor.
 14. The in-vehicle equipment according to claim 13, wherein the accumulating portion changes the charging switch from the off state to the on state at an end timing of a dead time just after the first switch is changed from the on state to the off state and changes the charging switch from the on state to the off state at a start timing of a dead time just after the second switch is changed from the on state to the off state.
 15. The in-vehicle equipment according to claim 12, wherein the accumulating portion includes a resetting portion configured to discharge the capacitor so as to reset the charge voltage of the capacitor.
 16. The in-vehicle equipment according to claim 1, wherein the controller includes: an error amplifier configured to generate an error signal corresponding to a difference between a voltage corresponding to an output voltage of the current mode control type switching power supply device and a reference voltage, a comparator configured to compare the slope voltage with the error signal so as to generate a reset signal as a comparison signal, an oscillator configured to generate a set signal as a clock signal of a predetermined frequency, and a timing control circuit configured to control on and off of the first switch and on and off of the second switch in accordance with the set signal and the reset signal.
 17. The in-vehicle equipment according to claim 1, wherein the second switch is a MOS transistor, and the current sensing portion senses the current flowing in the second switch by using a voltage between both ends of an on resistor of the MOS transistor.
 18. The in-vehicle equipment according to claim 5, wherein the controller includes: an error amplifier configured to generate an error signal corresponding to a difference between a voltage corresponding to an output voltage of the current mode control type switching power supply device and a reference voltage, a comparator configured to compare the slope voltage with the error signal so as to generate a reset signal as a comparison signal, an oscillator configured to generate a set signal as a clock signal of a predetermined frequency, and a timing control circuit configured to control on and off of the first switch and on and off of the second switch in accordance with the set signal and the reset signal, and wherein the constant period of time is set in a high level period of the set signal.
 19. The in-vehicle equipment according to claim 18, wherein the timing control circuit turns on the first switch when the set signal is switched from high level to low level, turns off the first switch when the reset signal is switched from low level to high level, and forcibly turns off the first switch and turns on the second switch regardless of a level changing state of the reset signal when the set signal is switched from low level to high level.
 20. The in-vehicle equipment according to claim 7, wherein the controller includes: an accumulating portion configured to accumulate current information sensed by the current sensing portion during a predetermined period of time while the first switch is in the off state, and a reflecting portion configured to start transmission of the current information accumulated by the accumulating portion before the first switch is changed from off to on so as to reflect the current information accumulated by the accumulating portion on the slope voltage.
 21. The in-vehicle equipment according to claim 20, wherein the accumulating portion and the reflecting portion are circuits driven by the same source voltage.
 22. The in-vehicle equipment according to claim 20, wherein the current sensing portion is a voltage current conversion circuit configured to convert the voltage corresponding to the current flowing between the first terminal and the second terminal of the second switch into current, the accumulating portion includes a capacitor to be charged by an output current of the voltage current conversion circuit, and the reflecting portion reflects a charge voltage of the capacitor on the slope voltage.
 23. The in-vehicle equipment according to claim 22, wherein the accumulating portion further includes a charging switch configured to make and break a current path from an output terminal of the voltage current conversion circuit to the capacitor.
 24. The in-vehicle equipment according to claim 23, wherein the accumulating portion changes the charging switch from off to on at an end timing of a dead time just after the first switch is changed from on to off and changes the charging switch from on to off at a start timing of a dead time just after the second switch is changed from on to off.
 25. The in-vehicle equipment according to claim 22, wherein the accumulating portion includes a resetting portion configured to discharge the capacitor so as to reset the charge voltage of the capacitor.
 26. The in-vehicle equipment according to claim 20, wherein the controller includes: a comparator configured to compare the slope voltage with the error signal so as to generate a reset signal as a comparison signal, an oscillator configured to generate a set signal as a clock signal of a predetermined frequency, and a timing control circuit configured to control on and off of the first switch in accordance with the set signal and the reset signal.
 27. The in-vehicle equipment according to claim 20, wherein the second switch is a MOS transistor, and the current sensing portion senses the current flowing between the first terminal and the second terminal of the second switch by using a voltage between both ends of an on resistor of the MOS transistor.
 28. The in-vehicle equipment according to claim 9, wherein the controller includes: an accumulating portion configured to accumulate current information sensed by the current sensing portion during a predetermined period of time while the first switch is in the off state, and a reflecting portion configured to start transmission of the current information accumulated by the accumulating portion before the first switch is changed from off to on so as to reflect the current information accumulated by the accumulating portion on the slope voltage.
 29. The in-vehicle equipment according to claim 28, wherein the accumulating portion and the reflecting portion are circuits driven by the same source voltage.
 30. The in-vehicle equipment according to claim 28, wherein the current sensing portion is a voltage current conversion circuit configured to convert the voltage corresponding to the current flowing in the diode into current, the accumulating portion includes a capacitor to be charged by an output current of the voltage current conversion circuit, and the reflecting portion reflects a charge voltage of the capacitor on the slope voltage.
 31. The in-vehicle equipment according to claim 30, wherein the accumulating portion further includes a charging switch configured to make and break a current path from an output terminal of the voltage current conversion circuit to the capacitor.
 32. The in-vehicle equipment according to claim 31, wherein the accumulating portion changes the charging switch from off to on at an end timing of a dead time just after the first switch is changed from on to off and changes the charging switch from on to off at a start timing of a dead time just after the diode is changed from on to off.
 33. The in-vehicle equipment according to claim 30, wherein the accumulating portion includes a resetting portion configured to discharge the capacitor so as to reset the charge voltage of the capacitor.
 34. The in-vehicle equipment according to claim 28, wherein the controller includes: a comparator configured to compare the slope voltage with the error signal so as to generate a reset signal as a comparison signal, an oscillator configured to generate a set signal as a clock signal of a predetermined frequency, and a timing control circuit configured to control on and off of the first switch in accordance with the set signal and the reset signal.
 35. The in-vehicle equipment according to claim 28, wherein the current sensing portion senses the current flowing in the diode by using a sense resistor connected in series to the diode. 